This invention is directed to particle identification and more particularly, to the identification of particles of one type located in a mass or ensemble of particles of various types, and the counting of the identified particles, if desired.
The herein described invention was developed for use in identifying and counting the number of biological cells of a given type present in a mass of cells of varying types and is described in that environment. In particular, the invention was developed for use in determining the percentage of reticulated (immature) blood cells, commonly called reticulocytes, present in a blood specimen. However, it will be appreciated from the following description that the invention has much broader applicability. For example, it can be utilized merely to identify cells or it can be used to identify and, if desired, count the number of biological cells of other types (such as leukocytes, platelets, and erythrocytes, etc.). Further, the invention can be utilized in pap smear analysis, and in other cancer screening operations.
The invention is also applicable to the identification and counting of particles other than biological cells. Further, the invention is useful in areas other than detecting defects or undesired (or desired) foreign bodies contained in a support medium. Hence, the use of the invention should not be construed as limited to the particular biological cell environment hereinafter described.
In recent years, various attempts have been made to develop methods of and apparatus for automatically identifying and counting biological cells and, in particular, the various biological cells contained in blood. For the most part, such attempts have been directed toward the identification and counting of leukocytes, although some attention has been given to the identification and counting of reticulocytes as well. In general, prior art attempts have been directed to the development of instruments for automatically analyzing blood cell images in a topographic manner. One prior art apparatus uses a high resolution microscope to magnify a conventionally stained blood smear illuminated by monochromatic light. A scanning detector such as a vidicon tube scans the magnified image. The output of the scanning detector is analyzed by a special purpose computer, or a suitably programmed general purpose computer, to provide the desired information. More specifically, the topology data contained in the scanning detector signal is sorted and analyzed by a series of algorithms to provide the desired information. Obviously, this apparatus is expensive and the method involved is time consuming, even considering the capabilities of modern digital computers. Moreover, highly skilled individuals are required to prepare the required program, if a general purpose digital computer is used. Further, a highly skilled medical technologist is still required to classify abnormal cells which the computer fails to recognize.
Another prior art proposal for identifying biological cells involves the suspension of the cells in a liquid. The suspended cells are carried through a flow tube where they interact with a focused laser beam. Information derived from the detection of the scattered light is analyzed by a suitable special purpose computer, or programmed general purpose computer. This approach is, obviously, also expensive and time consuming. First, the biological cells must be liquid suspended and, then they must be treated with a suitable material so that the flourescent properties of the cells to be detected are adequately enhanced. Finally, the material must be analyzed by expensive electronic equipment.
Another prior art biological cell identification and counting apparatus includes a continuous flow autoanalyzer. Cell identification is accomplished by spectrophotometrically analyzing differential cytochemical reactions, and by cell sizing. Again, this apparatus is expensive and its use is time consuming.
In general, the foregoing (except for the automatic microscope) and most other prior art methods and apparatus ignore the morphology (geometry) of the cells being analyzed. Rather, other cell parameters are emphasized, such as the interaction of a desired type of cell with a certain chemical or chemicals. The present invention, on the other hand, as will be better understood from the following description, places its main emphasis on cell morphology.
It will be appreciated from the foregoing brief discussion that the prior art apparatus for identifying and counting biological cells is expensive. In addition, the methods used are time consuming. Further, these methods and apparatus require the skill of highly trained personnel. Moreover, many of the prior art methods and apparatus are unsuitable for use in certain environments, such as the identification and counting of reticulocytes.
In view of the expensive nature of the prior art apparatus and their unsuitability in many environments, classical manual techniques for identifying and counting biological cells remains widespread. In the particular case of reticulocytes, the classical techniques involve incubating a few drops of blood with a suprevital stain (such as New Methylene Blue). Thereafter, thin smears are prepared and, by light microscopy, the number of reticulocytes among a predetermined number of red cells (such as 1,000 or 5,000) are manually counted. The end result is a percentage number representing the percentage of red blood cells that are reticulated. Not only is this technique tedious and time consuming, but it is also limited in accuracy. A recent study by the National Communicable Disease Center showed that performance was unsatisfactory in 40% of the laboratories tested with respect to the differential classification of blood cells on normal blood smears, and unsatisfactory in an even greater percent of the laboratories when the test specimens were blood smears from certain frequently encountered abnormal conditions. Thus, it is desirable to provide a method of and an apparatus for achieving the desired information without requiring such tedious and time consuming labor, along with equal to or better accuracy, not only for use in identifying and counting reticulocytes, but also for use in identifying and counting other types of biological cells and particles.
Therefore, it is an object of this invention to provide a method of and an apparatus for identifying the particle or particles of a given type located in an ensemble of particles of varying types.
It is a further object of this invention to provide a method of and an apparatus for identifying the particle or particles of a given type located in a ensemble of particles of varying types and either counting the particles or determining their concentration with respect to particles of some other given type.
It is also an object of this invention to provide a method of and an apparatus for identifying and counting the biological cells of a given type present in a mixture or ensemble of biological cells of various types.
It is another object of this invention to provide a method of and an apparatus for determining the percentage of reticulated red blood cells present in a blood specimen.
It is a further object of this invention to provide an inexpensive apparatus suitable for rapidly identifying and counting the number of particles of a given type present in an ensemble of particles of various types.
It is yet another object of this invention to provide an inexpensive apparatus suitable for rapidly identifying and counting the number of biological cells of one type in an ensemble of biological cells of varying types, and in particular the number of reticulated red blood cells in a blood specimen.
During the development of the main method and apparatus of the present invention, it was found necessary to produce an optical filter having minimum mean-square error linear characteristics. Thus, it is a subsidiary object of this invention to provide a method of producing a minimum mean-square error linear optical filter, and the filter obtained thereby.